The present invention relates generally to a method for confirming that a memory other than a main memory, e.g. ROM is incorporated into a computer system.
Recently, a control system has been developed which controls the entire operation of an internal combustion engine by using a microcomputer. Such microcomputer control system generally comprises:
(a) a Read Only Memory (usually abbreviated as ROM);
(b) a Central Processing Unit (usually abbreviated as CPU) which fetches a series of instructions (a program) from the ROM, performs arithmetic and logical operations on data inputted via an input interface circuit and/or data stored in the ROM or RAM (described below) in accordance with the fetched instructions, and feeds the arithmetic result to an output interface circuit where the digital arithmetic result is converted into various output signals;
(c) a Random Access Memory (usually abbreviated as RAM) which temporarily stores provisional data required for completion of arithmetic and/or logical operations, the meaning of the term "random access memory" being derived from a storage technique in which the time required to obtain information is independent of the location of the information to be obtained;
(d) Input/Output devices which send or receive various data to or from the CPU via the Input/Output interface circuit; and
(e) buses, including a data bus, address bus, and control bus, which provide means for transferring various data, instructions, and control signals between the above-listed units.
In such a microcomputer control system it is sometimes necessary during program execution to confirm that an auxiliary ROM in which updated or modified data, or an instruction sequence is written, or RAM is, incorporated both physically and through programming into the microcomputer system through installation in a proper receptacle.
For example, in a microcomputer control system which uses mask ROM as a master ROM, an auxiliary ROM of small capacity which stores revisions for some of the contents of the master ROM may be provided for modifying or altering the stored contents (program or data) of the master ROM. For that purpose, the microcomputer needs access to the auxiliary ROM before reading the portion of the contents to be altered. Since in such a microcomputer control system the execution sequence of the program will be corrected only when the auxiliary ROM is incorporated into the system, it is necessary to confirm that the auxiliary ROM is incorporated into the system; otherwise, the CPU executes the original program routine in the master ROM.
In prior-art systems in which confirmation such as that described above is required, a means for generating a confirmation signal to detect whether the auxiliary ROM is incorporated into the system is used. The confirmation signal from an input device is inputted into the microcomputer system via the input interface circuit and the program sequence is changed after confirmation as described above.
However, the conventional method described above requires a means for generating the above-described confirmation signal so that the microcomputer control system becomes more complex and the number of input signals to be handled by the input interface circuit becomes greater, and thus the input interface circuit becomes more complex.